An urgent review is underway after a Four Corners investigation found elevated levels of dangerous dioxins in a generic version of 2,4-D, one of Australia's most widely used herbicides.

Dioxins are one of the most deadly chemical compounds in the world, but Australian authorities do not routinely test for them.

One scientist said the product tested by Four Corners, which was imported from China, had one of the highest dioxin readings for 2,4-D in the last 10 to 20 years, and could pose potential health risks.

The regulator – the Australian Pesticides and Veterinary Medicines Authority (APVMA) – has urgently referred the Four Corners test results to the Office of Chemical Safety for assessment.

"The APVMA is always concerned about allegations of undeclared impurities found in registered products," APVMA chief executive Kareena Arthy said.

However, a spokesperson for the company which owns the product tested by Four Corners said the APVMA did not have any guidelines for dioxins in 2,4-D.

Common product used to combat weeds

To help combat Australia's $4 billion weed problem, more than $100 million worth of 2,4-D products are sold each year in Australia.

Many now have their active ingredient imported from countries like China, India and Argentina.

It was assumed that because of improved manufacturing processes that there were no longer any dangerous dioxins in 2,4-D.

Matthew Cossey, the spokesperson for Croplife Australia, a peak chemical body which represents many major chemical companies, says a regulatory system should have an independent testing regime for substances like dioxins.

"I'd be concerned that in fact the regulator is not maybe paying enough attention to the new players in the industry to imports and ensuring that they're coming from reliable, accredited, recognised suppliers," he said.

Researcher says results should be a wake-up call

Lee Bell, a researcher with the National Toxic Network, says it is a wake-up call for the regulator.

"We've been told many, many times over the years that industry has cleaned up its act, that they have new processing equipment, new techniques, new technology that will eliminate dioxin from their herbicides and therefore from our environment," he said.

He said the results show that the industry has not come clean about dioxins in 2,4-D and the Government should act immediately to protect human health.

Watch Four Corners tonight for more on the legacy of herbicides 2,4,5-T and 24D, which reportedly killed many Australians who sprayed the dioxin-contaminated chemicals in the 1970s and 1980s.